1. Field of the Invention
The present invention relates to a light emitting device including a light emitting element and a phosphor layer, and a method for manufacturing the same.
2. Description of the Related Art
Generally, a light emitting device using a light emitting element such as a light emitting diode (LED) has electronic parts such as a light emitting element and a protection element, a substrate on which the elements are positioned, and a transparent resin for protecting the light emitting element, the protection element and the like.
A technique is known in which, for the purpose of causing the light emitting device to emit white light, a concave portion is provided on the substrate, a light emitting element for emitting blue light is positioned in the concave portion, and a transparent resin including a phosphor is provided so that the phosphor covers the light emitting element in the concave portion. In the light emitting device, a wavelength of a portion of the blue light output from the light emitting element is converted by the phosphor, and yellow light resulting from the wavelength conversion is mixed with the blue light from the light emitting element, thereby emitting white light. However, in this way, it is hard to obtain uniform white light because a difference occurs in the quantity of blue light absorbed by the phosphor according to difference in a length of an optical path of the blue light from the light emitting element. Since the phosphor included in the transparent resin in the concave portion is excited to emit light, a light emitting area becomes larger.
On the other hand, JP-A-2003-69086 discloses a method for forming a phosphor layer having a uniform thickness on the light emitting element by using a so-called electrodeposition method. Accordingly, difference in the length of the optical path of the blue light can be reduced. In the light emitting device provided with the phosphor layer formed thereon by the electrodeposition method, the light emitting device can have light distribution characteristics close to that of a point light source since the phosphor layer can be formed very near to the light emitting element. The point light source has an advantage of enabling easy design of an application product to which the point light source is installed since the point light source has a small light emitting area. Accordingly, an expansion of the use thereof is expected in various fields including the lighting apparatus field.
In the electrodeposition method, the phosphor particles deposit on a surface of the light emitting element by applying an electric field in a bath liquid containing phosphor particles deposits. However, according to the electrodeposition method, an electrically conductive wiring pattern exposed around the light emitting element is also covered with the phosphor particles. Therefore, light emitted from the phosphor layer provided on the surface of the light emitting element may be absorbed by the phosphor layer provided on the wiring pattern around the light emitting element. Further, light emission from the phosphor layer provided on the wiring pattern may induce uneven light emission.
JP-A-2003-69086 proposes forming a photoresist on the wiring pattern so as to prevent the phosphor particles from adhering onto the wiring pattern. However, the proposal requires additional steps for forming and removing the photoresist. Further, in JP-A-2003-69086, the light emitted from the light emitting element is absorbed by the wiring pattern around the light emitting element, which lowers light extraction efficiency.
In many cases, the light emitting element is bonded to a substrate by way of a metallurgy bump and the like. In the bonding process, a small space is created between the light emitting element and the substrate. It is difficult to completely fill the space between the light emitting element and the substrate with the phosphor particles, and thus a density of the phosphor particles tends to be lower than that of the other areas. As a result, light from the light emitting element may leak therefrom.